Conventionally, as a material of an electrode and a wire (hereinafter, referred to as an electrode/wire) in electrical/electronic equipment, noble metal (e.g., copper, silver and gold) or its alloy has been often used. In general, solder joining is adopted for electrical joining of the electrode/wire. The joining portion has favorable electrical conductivity and reliability. Solder joining is also often used for heat dissipation joining of a power semiconductor module or the like in addition to the aforementioned electrical conductive joining.
Recently, there has been a trend to change the material of the electrode/wire from noble metal to aluminum (Al) or its alloy because of a strong demand for a reduction in weight and cost of the electrical/electronic equipment. However, the Al and an Al alloy tend to form a chemically stable oxide film on their surface and thus have low solder wettability. Therefore, there is a problem that it is difficult to ensure highly electrical conductive and reliable joining by solder joining. Thus, when the Al or an Al alloy is used as a material of the electrode/wire, conventionally, electrical conductive joining is often carried out by swage joining, ultrasonic joining, or the like. However, the swage joining or the ultrasonic joining has a drawback of being inferior to the solder joining in terms of workability, mass productivity, and long-term reliability.
Given the above background, various types of new electrical conductive joining that can ensure electrical conductivity comparable to that of the solder joining with respect to noble metal even in the case of a hard-to-solder joinable metal, e.g., Al, have been studied. For example, Patent Literature 1 (JP 2014-184474 A) teaches a joining material including a vanadium oxide-containing low-melting glass and electrical conductive particles (metal particles), as an electrical conductive joint material that replaces a solder material of conventional art. According to Patent Literature 1, the use of such joining material enables joining of an electric wire of aluminum or an aluminum alloy to a joined metal with electrically and mechanically high connection reliability.